Providing a vital link between internal and external clouds, VMware plans to release in March an adapter for moving virtual machines between a hosted service offering and an organization's own internal systems, the company announced Tuesday.

In addition, the company announced that three service providers -- BlueLock, Colt and Verizon -- are now offering cloud hosting services that VMware has certified to work with its vCloud software. Organizations will be able to use the connector to move their virtual workloads between their own VMware-based private clouds and these public cloud services.

"The software makes it as easy as possible for VMware's customers to extend their data centers into the cloud," said Matthew Lodge, VMware senior director of cloud services.

First previewed during VMware's VMworld conference last August, the VMware vCloud Connector will be a plug-in for users of the company's vSphere software. "The plug-in extends the console so they now can see machines running in the cloud," Lodge said. Both external and internal VMs can be observed through "a single pane of glass," he said.

Most of the actions that an administrator can do to a local VM can also be executed against an external cloud VM by using the connector. Workloads can even be moved between an internal and external cloud.

The software does have some limitations, Lodge admitted. Actions involving changes in physical infrastructure can't be completed against cloud services, such as decommissioning servers, because the provider controls those aspects of the service. Also, in order to be moved, VMs must be halted and then restarted at the new location; live migration is not possible yet, Lodge said.

Users must have version vSphere 4 or vSphere version 4.1 in order to use the plug-in. However, an organization does not need to be running a private cloud in order to use the connector. "You can just extend vSphere out to a public cloud provider," Lodge said.

The connector should work with any hosting provider running vCloud and vSphere Director, and is guaranteed to work with any public hosting services that have been certified through the VMware vCloud Datacenter Services program, which assures that the provider has correctly implemented vCloud API (application programming interface) and support for the OVF (Open Virtualization Format) format.

BlueLock, Colt and Verizon are the first three companies to be certified under this program, which VMware also announced last August. Verizon is offering VMware cloud services globally, while BlueLock is offering cloud services in the U.S. and Colt is offering them for Europe.

VMware's approach to encouraging greater use of its platform for cloud deployments differs from that of its chief competitor in this space, Microsoft, and its Azure platform. Microsoft offers a hosted version of Azure and it also licenses partners to run their own versions. VMware is not offering its own hosted service and instead relies entirely on external providers.

"We are completely partner-led. We're not going to compete with our service providers," Lodge said. "You get a delivery with service providers who are in a local marketplace and can support you directly."

The connector will be available sometime "in March" and will be free, Lodge said. The company estimates that 250,000 copies of vSphere are now in use.